Washington (CNN)President Barack Obama on Sunday forcefully declared the shooting in San Bernardino, California, a terrorist attack and said the United States will overcome such threats with a relentless, strong and smart campaign against ISIS that is consistent with the nation’s values.

“This was an act of terrorism designed to kill innocent people,” Obama said during a rare prime-time televised speech from the Oval Office.

Obama, speaking from a podium in front of his desk in the Oval Office, said the couple that had carried out the San Bernardino attack had “gone down the dark path of radicalization” and embraced a “perverted version of Islam” that calls for a war against America and the West.

The address was designed to reassure Americans about the rising threat from terrorism and essentially argued for staying the course. It was delivered amid concerns that Obama does not have a plan sufficient to address the crisis, following the mass shooting in which 14 people were killed by a self-radicalized Muslim couple.

“The threat from terrorism is real, but we will overcome it. We will destroy ISIL and any other organization that tries to harm us,” Obama said, using an alternative name for the extremist group that has carved out a self-declared caliphate in Syria and Iraq and now appears to be turning its sights on the West.

“We will prevail by being strong and smart, resilient and relentless,” Obama said, calling on Congress to take action to outlaw anyone on a terrorist “no fly list” from buying weapons and asking lawmakers to pass a final authorization for U.S. armed forces to wage war on the group.

In an appeal that will likely anger conservatives, Obama demanded greater gun control in his address, saying it was a key part of combating ISIS. He said it is currently too easy for people who want to harm Americans to buy guns.

“Congress should act to make sure no one on a no- fly list is able to buy a gun. What could possibly be the argument for allowing a terrorist suspect to buy a semiautomatic weapon? This is a matter of national security,” Obama said, and also argued it should be harder to buy powerful assault weapons like those used in the San Bernardino attacks.

“What we can do, and must do, is make it harder for them to kill,” Obama said.

Terrorism, national security and the place of Muslims in U.S. society have become a contentious 2016 campaign issue and are dominating the political conversation more than at any time since the September 11 attacks in 2001.

In a new CNN/ORC poll released on Sunday, 60% of Americans disapproved of Obama’s handling of terrorism — up nine points since May. Two thirds of those polled, meanwhile, said they disapproved of the president’s handling of ISIS.

The poll was conducted before the attacks in San Bernardino and also showed a shift in public opinion on how to tackle the group with a majority — 53% — for the first time saying the U.S. should send ground troops to fight ISIS. And 68% said the American response to the group’s rise had not been sufficiently aggressive.

Those figures reflect Obama’s struggle so far to convince critics he has a viable strategy for destroying ISIS in its self-declared caliphate in Iraq and Syria. Obama has also been accused of downplaying the threat from the group for political reasons.

He went into the speech under intense pressure to strike a rhetorical note equal to the moment, following a string of comments about ISIS that left him vulnerable to claims by opponents that he had not taken the group’s rise seriously.

Obama has variously referred to ISIS as a “JV” team, said it was “contained” and described its fighters as “killers with good social media” despite its widening footprint in the Middle East and apparent turn to attacking soft Western targets in recent weeks.

Republicans have redoubled attacks following the California killings to fire up a hawkish party base ahead of early nominating contests and to suggest that Obama’s policy isn’t working and that the president does not understand the threat.